Motor housing having simplified cover plate and brush base

ABSTRACT

An end assembly for a miniature motor. The end assembly including a brush base, a pair of brush arms supporting brushes, and a cover plate supporting a rotor bearing. The end assembly fits into an open end of a cylindrical motor housing.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of Provisional Application No.60/238,019, filed Oct. 6, 2000, the entire content of which is herebyincorporated by reference in this application.

FIELD OF THE INVENTION

The invention relates generally to miniature motors used in, forexample, toys; audio and video equipment, and automotive electricalappliances, hand tools and other motor-driven devices. Moreparticularly, the invention relates to an end cover plate and brush basefor a motor casing of a miniature motor.

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT

FIG. 1 is a miniature motor 10 having a metallic cylindrical housing 12.The housing 12 may be formed of mild steel and have a hollow tubularsection 14 and an integral bottom 16. The opposite end 30 of the housingis open to receive a brush base and cover plate at one end of thetubular section. Within the housing are fixed a pair of oppositepermanent magnets 18, each of which have an arc shape to match the innerwall of the housing. The magnets form between them a volume in thehousing for a rotor 20. The rotor includes a cylindrical armature 22coaxially mounted on a rotor shaft 24. The rotor shaft 24 extendsthrough the opposite ends of the housing 12.

Bearings 26 are mounted to rotatably support the shaft in the ends ofthe housing. The bottom 16 of the motor housing has an integral flange28, into which is press-fitted a bearing 26 to support one end of therotor shaft 24. The opposite end 30 of the housing has an opencylindrical base which receives a brush base 32 and cover plate 34 whichare assembled together to fit in the open end 30 of the housing.

The cover plate 34 fits over the base, and the cover plate and brushbase fit into the motor housing. The open edge of the housing is crimpedonto the plate. The cover plate 34 has a flange 36 to support a bearing26 which supports an end of the rotor shaft 24. The flange 36 andbearing 26 of the cover plate 34 (when inserted in the motor housing)are coaxially aligned with the flange 28 and bearing 26 on the bottomsection 16 of the motor housing so that the rotor shaft is held incoaxial alignment with the motor housing 12.

The brush base 32 supports a pair of brush arms 38 which provide anelectrical connection between an external electrical contact 40 of themotor and the armature 22 of the rotor 20. The brush arms are generallystrips of copper having a first end fixed to the periphery of the brushbase 32 and an opposite, free end on which is mounted a brush 42. Thebrush arms are attached to opposite sides of the brush base. The brusheson the arms face each other at the axis of the motor. When inserted inthe housing, the brushes are in slidable contact with the commutator 44on the rotor shaft 24. The commutator provides an electrical contactbetween the wiring of the armature 22 and the brushes.

The external contacts 40 of the brush arms provide direct electricalcurrent (D.C.) through the brushes and the commutator to the windings inthe armature 22. Electrical current flowing through the armature createsan alternating magnetic field within the housing that interacts with themagnetic field of the permanent magnets 18. This interaction of magneticfields creates a force that rotates the rotor 20. This rotation drivesthe rotor shaft 24 to provide a mechanical rotational output powersource from the rotor. The rotor shaft 24 extends through the bottom 16of the housing to provide a mechanical power output to drive a gear boxor other device.

Conventional cover plates 34 are cylindrical discs having embeddedrecesses which fit into matching slots in the brush base 32 and/orgrooves in the end 30 of the housing. Forming a motor plate havingrecesses, brush bases having slots and machining the motor housing tohave the grooves needed to match the cover plate and/or base adds to thecomplexity and cost of miniature motors. Miniature motors tend to be arelatively-low cost component of toys and other equipment. Accordingly,it is important that manufacturing costs for making these motors beminimized.

SUMMARY OF THE INVENTION

The invention is intended to overcome the problems inherent with priorminiature motors having complicated brush bases, and motor plates.Specifically, the invention relates to a simplified construction of amotor housing, brush base and motor plate.

The simplified construction features include a motor housing having anouter end which has a smooth circular edge, that does not require thecutting of slots into the edge. Minimal machining may be applied to theedge to polish an outer ring of the housing and to machine a lip toengage the brush base. The brush base also has a simplified constructionand formed by injection molded plastic. Moreover, the brush base hasseveral features which facilitate the assembly of the motor housingincluding a collar and flange that fit easily into the motor housing tofix the position of the brush base inside the housing. The cover plate,which may be a simple metal stamp construction, fits directly onto aplanar region of the brush base.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cross-sectional side view illustrating an example ofa conventional miniature motor.

FIG. 2 is an exploded view of a motor casing, brush base and motorplate.

FIG. 3 is an end view of a motor casing assembled with a brush base andmotor plate.

FIG. 4 is a side view of the brush base shown in FIG. 2.

FIG. 5 is an inside end view of a brush base.

FIG. 6 is a cross-sectional diagram of the brush base shown alongsection line 6—6 in FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2 shows an exploded view of a motor housing 50, a brush base 52 anda motor cover plate 54. The housing 50 is a cylindrical metallic steelshell having an open end 56 and a closed bottom end 58. An advantage ofthe motor housing 50 is that the open end 56 has a smooth circular edgewhich is easily fabricated and does not require specialized machining toform grooves, slots or other shapes in the edge. By eliminating thegrooves, slots or other shapes at the edge, the circular edge of the end56 is a smooth surface, with good roundness. The outer surface of thehousing may be formed at ring 60, which extends approximately 0.25 inchfrom the outer edge 56 of the housing.

The inside surface of the housing includes an annular lip 62, whichengages a pair of flange sections 64 of the brush base. The annular lipis a ring on the inside surface of the housing, adjacent to the edge 56,and having a diameter slightly greater than the inside diameter of thehousing. The ring may have a rounded shoulder at the transition betweenthe ring and the rest of the inside surface (having a smaller diameter)of the tubular housing. A rounded shoulder may provide a better grip onthe flange 64 of the base holder, which is entirely in a plane normal tothe axis of the housing. The formation of a smooth and continuous edge56 of the housing having an outer polished ring 60, and an inner lip 62with good roundness is relatively simple and inexpensive.

FIG. 3 shows the brush base 52 and motor cover plate 54 inserted in theopen end 56 of the housing. The brush base and cover plate are coaxiallyaligned with the housing. To secure the brush base in the housing, acrimping tool (not shown) makes small indentations 66 on the outer edge56 of the casing. These indentations bend inward to the edge 56 of thehousing to fix the brush base 52 and cover plate 54 to the housing. Theindentations 66 in the housing edge 56 are aligned with the base and thecover plate to hold both the base and plate in the housing, and tolocate the relative position between the brush base and housing withoutany rotation. The outer diameter of the brush base 52 slides inside theinside diameter (beyond the lip 62) of the housing 50 by way of aninterference fit. The flanges 64 of the base slide in the housing untilthey engage the lip 62. The lip has a diameter slightly larger, e.g., byone or more tenths of an inch, than the inside diameter of the housing.The flange and lip engagement prevents the brush base from slidingfurther into the housing. The engagement of the flanges 64 and lip 62,and the crimping 66 of the edge of the housing onto the brush base andcover plate, the brush base is held securely within the motor casing 50.

FIG. 4 shows a side view of the brush base 52. The base includes anannular collar 70 that has an outside diameter substantially the same asthe inside diameter (below the lip 62) of the housing 50. The outside ofthe brush base may include at least one vertical slot 75. The brush baseis formed of a plastic material having relatively high rigidity andstrength, and a large dielectric constant to provide electricalinsulation. The collar may include a pair of opposite vertical slots 73to receive a grounding element to the housing when assembled. The slotmay extend substantially the height of the collar, except for the flange64 continues across the slot. These slots 73 may not be necessary forsome motors. The outer end 72 of the base 52 includes a recessed centerplanar section 74 that provides a platform on which the cover plate 54lies. The planar region 74 has a semi-rectangular opening (76 in FIG. 5)to provide open access through which extends the rotor shaft. To assistwith attaching the motor plate 54 to the brush base 52, the planarregion 74 includes small posts 68 which fit into matching apertures 78in the cover plate. The plate is fitted onto the planar region 64 andsnapped onto the posts 68. To secure the plate, the outer tips of theposts 68 may be press fit to form a rivet-type connection holding theplate onto the brush base.

The outside end 72 of the brush base also includes a pair of oppositeplateau-flanges 64 that are slightly elevated above the planar region.Each plateau-flange has an inner straight edge 80 that borders the coverplate, and an outer arc-shaped edge that slightly overhangs the collar70 of the brush base, e.g., by about a tenth of an inch. The overhang ofthe flange abuts against the lip 62 of the housing, when the base isinserted in the housing. Thus, the overhang should extend beyond thecollar by approximately the same distance as the width of the lip in thehousing. The flanges are each a relatively thick portion of the base andinclude slots through which extend the electrical contacts 82 for themotor.

The inside end 84 of the brush base 52 slides into the housing. A pairof magnet posts 86 extend downward from the end 84 of the base and abutagainst the permanent magnets 18 fixed to the inside wall of the motorhousing. These posts 86 insure that the permanent magnets and the brushbase remain properly separated in the motor housing.

FIG. 5 shows a bottom view of the brush base 52 and FIG. 6 shows across-sectional view of the brush base through section line 6—6. Toprovide structural support for the magnet post 86, a pair of postsupports 88 are formed in the brush base integral with the collar 70.Similarly, an arm support 90 is integrally formed with the collar andprovides a support for a pair of the brush arms 92. The arm base 90includes slots to receive the end of the brush arm, and to provide anelectrical connection with the external connector 82.

Each brush arm 92 is formed of a highly conductive metal, such ascopper, and extends from the base 52 towards the center of the brushbase. The arm may have a shallow U cross-sectional shape to providestructural rigidity to the arm. At the free end of each arm (towards thecenter of the motor) is attached a conductive brush 94. The arm forms acantilevered beam that holds the brush and biases against thecommutator. The brushes are rotatably and slidably in contact with thecommutator of the motor and provide the electrical connection betweenthe rotor and the external power contacts.

The brush base 52 is an integral plastic component that is injectionmolded. The external connectors 82, brush arms 92 and brushes 94 arefastened to the brush base 52 to form a complete component ready forassembly in the motor. The cover plate 54 is a flat metallic plateeasily formed. As shown in FIG. 3, the plate has a semi-rectangularouter shape, including a pair of opposite straight edges which are inabutting contact with the flanges 64 of the base. The other pair ofedges of the plate are arc-shaped to match the curvature of the open end56 of the motor housing. The plate also includes a center circular plate96 that is slightly raised to provide structural support for the bearingflange 98. This flange supports the rotor bearing 26 and the rotor shaft24.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. A motor comprising: a cylindrical housing havingan open end with a circular edge and a lip on an inside surface of thehousing; a brush base having an annular collar which fits into the openend of the housing and past the lip, an outside end of the collarincludes a recessed planar region defined by a pair of opposed plates,wherein the plates rise above the annular collar and overhang aperiphery of the collar such that the plates abut the lip when the baseis inserted in the housing to position the brush base in the housing,and a cover plate sized to fit on said planar region of the brush base,said cover plate having an annular flange to support a rotor bearing. 2.A motor as in claim 1, wherein said brush base further includes a pairof brush arms supporting brushes.
 3. A motor as in claim 2, wherein thebrush base further includes external connectors attached to the brusharms, extending through the base and protruding outwardly from theoutside end of the collar.
 4. A motor as in claim 1, wherein the brushbase is formed of plastic and the cover plate is metal.
 5. A motor as inclaim 1, wherein the planar area has posts which insert into aperturesof the cover plate, and the posts are permanently press fit to securethe cover plate.
 6. A motor as in claim 1, wherein the annular collarhas a circular cross section.
 7. A motor as in claim 6 wherein thecollar has an outer peripheral surface form a substantiallyuninterrupted annular surface.
 8. A motor as in claim 7, wherein saidouter peripheral surface of the collar is interrupted by a pair ofnarrow vertical slots in the surface.
 9. A motor as in claim 1, whereinthe cover plate is a semi-rectangular plate having a raised disk withthe annular flange.
 10. A motor as in claim 1, wherein the circular edgeof the cylindrical housing includes crimping to hold the cover plate onthe brush base.